1. Technical Field
The present invention relates to a thrust bearing arrangement for a turbocharger.
2. Background Art
The present assignee/applicant proposed various thrust bearing arrangements for turbochargers. For example, such thrust bearing arrangements are disclosed in Japanese Utility Model Applications, Laid-Open Publication Nos. 4-119624 published Oct. 26, 1992, 5-12634 published Feb. 19, 1993 and 5-12635 published Feb. 19, 1993. The arrangement of Japanese Publication No. 4-119624 is shown in FIG. 3 of the accompanying drawings. FIG. 3 illustrates a compressor side of a turbocharger "s". A thrust bearing unit "a" includes a normal thrust bearing "b" and a reverse thrust bearing "c". An oil feed passage "e" extends through a bearing housing "f" and the normal thrust bearing "b" and opens to a pad face "d" of the normal thrust bearing "b". An oil supplied to the normal thrust bearing "b" from the passage "e" is further guided to a pad face "h" of the reverse thrust bearing "c" by a guide element "g" which is part of a bearing housing "f". A turbine shaft "i" has a thrust bushing "j" of L-shaped cross section and fitted thereon. The thrust bushing "j" is interposed between the normal thrust bearing "b" and the reverse thrust bearing "c" and serves as a thrust member for the turbine shaft "i".
During operation of the turbocharger "s", the turbine shaft "i" generally tends to move to the right in the drawing (i.e., normal thrust direction) and the thrust bushing "j" is often forced against the pad face "d" of the normal thrust bearing "b". In such a situation, an oil is directly supplied to the pad surface "d" for lubrication. On the other hand, when the turbine shaft "i" moves to the left (i.e., reverse thrust direction) and the thrust bushing "j" is correspondingly forced against the pad surface "h" of the reverse thrust bearing "c", the oil guided by the guide "g" lubricates the pad surface "h". In this manner, both the normal and reverse thrust bearings "b" and "c" are lubricated effectively. Appropriate lubrication results in prevention of deterioration in performances of the turbocharger "s" due to friction loss.
The turbine shaft "i" has an oil thrower "k" and a compressor wheel "p" fitted thereon respectively next to the thrust bushing "j" in the rightward direction of the illustration. The oil thrower "k" has a radially enlarged slinger portion "m" whose one face is exposed to the normal thrust bearing "b" with a certain clearance. The other face of the slinger portion "m" on the compressor side is exposed to an oil deflector "o" with a certain gap. The oil deflector "o" is clamped between the bearing housing "f" and a sealing plate "n". Combination of the slinger "m" and the oil. deflector "o" prevent oil leakage toward the compressor. The slinger "m" disperses the oil and the oil deflector "o" collects the dispersed oil and guides it to an oil drain (not shown). The turbocharger "s" has also a turbine wheel (not shown) on the left side of the turbine shaft "i".
SUMMARY OF THE INVENTION
The inventor found by experiments that a necessary and sufficient amount of oil was generally supplied to the thrust bearings "b" and "c" in the conventional arrangement shown in FIG. 3 of the accompanying drawings, and that amount was very small. Thus, there was no substantial oil leakage even when the slinger "m" and the oil deflector "o" were dispensed with. In particular, if the oil thrower "k" does not have the slinger "m" which is a rotating element, a moment of inertia is reduced. Reducing the moment of inertia results in improvement of the turbocharger performances.
On the other hand, it is of course preferred for the sake of safety and reliability that the thrust bearing arrangement is equipped with a means for preventing oil leakage.
An object of the present invention is to propose a thrust bearing arrangement for a turbocharger which does not have a slinger and an oil deflector but is equipped with an alternative means for preventing oil leakage, which alternative means exerts a less moment of inertia (particularly the moment of inertia at a position of the slinger "m" is reduced).
According to one aspect of the present invention, there is provided a thrust bearing arrangement for a turbocharger, comprising a thrust bearing unit having separate normal and reverse thrust bearings spaced from each other in a longitudinal direction of a turbine shaft and spaced from the turbine shaft in a radial direction of the turbine shaft, a bearing housing for housing the thrust bearing unit, a thrust member provided on the turbine shaft and interposed between the normal and reverse thrust bearings, with a lubrication oil being supplied to a first contact area between the normal thrust bearing and the thrust member, a guide portion formed on the bearing housing for further supplying the lubrication oil to a second contact area between the thrust member and the reverse thrust bearing, and a seal member provided on the turbine shaft in slidable contact with an inner peripheral face of the normal thrust bearing.
The seal member prevents leakage of the lubrication oil from the thrust bearing arrangement. In addition, an outer diameter of the seal member is generally smaller than an inner diameter of the normal thrust bearing. It other words, the seal member is positioned radially inward of the normal thrust bearing. Thus, a lower moment of inertia is generated as compared with a conventional arrangement having a radially enlarged member.
The guide portion of the bearing housing may completely surround the thrust member circumferentially with a certain gap to define an oil chamber around the thrust member, and a passage may be formed in the bearing housing which extends to a turbine side of the turbocharger from the oil chamber. The lubrication oil is supplied to the first contact area. On the other hand, the lubrication oil supplied to the floating metal or radial bearing eventually reaches the second contact area. The lubrication oil is further transferred to near the turbine (e.g., an oil jacket for the turbine) by the passage to cool the turbine. In this manner, the lubrication oil is used effectively. The bearings on the turbine side, the seals and the turbine are also cooled by the lubrication oil. Cooling the turbine improves performances of the turbocharger.